Timothy Keanini, chief technology officer of nCircle, loves Mac - just not in his company (a maker of network security and compliance management tools).

Keanini has been both a Mac user and a Mac developer during the past five years. Starting in 2001, he brought Macs into his 100-person company (starting with an Apple G4 notebook for himself) because he believed the user-friendly interface and ability to work in a Unix-like environment would help productivity among the engineering team.

So Keanini, who handled IT decisions until the company grew large enough to bring in a director of IT in 2005, encouraged and officially supported nCircle's approximately 40 engineers using MacBooks.

"The rest of our company was Windows, but engineering was mainly Macs because of me," he says.

But ultimately, instead of productivity gains, dealing with compatibility issues between the Macs used by the engineers and the PCs running Windows used by the line-of-business people in the office slowed down work and resulted in communications issues, he says.

So while Apple's sales continue to grow, Keanini decided to buck the trend, and gave up on his most recent Apple machine, an Intel dual-core based MacBook Pro.

"Between four and six months ago I switched back to Windows," he says. While Apple's installed base is growing, he left the camp he had once espoused to others. He also now advocates that his company's engineers get Windows machines. Even at his home, Apple's role has changed.

"I am all PC at home and at work now, because frankly if I'm not working, I'm gaming. And the Mac doesn't have games," Keanini says, though his household still has three Apple machines in use by other family members.

What makes an Apple loyalist change camps? Here's a look at five reasons why one tech chief did just that.

1. Productivity Trumps Religion

It's easy to fall in love with the aluminum cases used in Mac hardware and the slick interface design of the Mac OS X, Keanini says. Those are two reasons why more people are moving to Apple products: Apple announced shipments of its personal computers grew by 44 percent in the first quarter of 2008, beating the 15 percent growth in PC shipments worldwide, according to market researcher IDC.

Yet, depending on how a company uses Macs, trying to integrate the computers into a company's workflow can kill productivity, Keanini says. The applications never quite match up, data has to be massaged to be useful, and the company has to design workarounds for each issue, he says.

"My rule is to find the technology that makes your company most productive and be honest with yourself about it," he says. "Don't bring religion into it."

2. Workarounds Waste Time

As soon as a company allows a different operating system onto workers' desks, employees have to start dealing with all the little problems that crop up. Calendar programs no longer synch with the rest of the company and documents created in one office software suite have to be converted to another, usually Microsoft Office. If your company uses Microsoft Exchange, as Keanini's does, this adds another layer of problems.

"Everything is going to be a little bit different, and that little difference in everything eventually adds up," Keanini says.

One company engineer woke up Keanini the night before presentation slides were due for a conference, his voice cracking with stress, because his slides-exported from Apple's Keynote presentation application to Microsoft PowerPoint-looked nothing like they had on the Mac.

While such mistakes can be avoided, the work required to keep the company's data working on two platforms eventually saps productivity gains, he says

3. It's Hard to Abandon Favourite Tools

You may become quite attached to a Windows application or two, and decide Apple doesn't have a comparable equivalent. Apple is well known for creating user friendly applications, but for Keanini, Microsoft has a lead with at least one program: OneNote, which he uses for personal information management.

The application, originally created for Microsoft's tablet PC platform, allows the user to bring all sorts of data into a single notebook format. Also, OneNote does not have a save dialog box, Keanini says. Microsoft recognizes that, if a user enters data into their computer, they are going to want to save it.

Keanini finds himself using OneNote as an organizational hub for his day.

"It integrates so well from Office," Keanini says. "I can send mail from it, I can do To-Dos from it. Bottom line, does it make me more productive? Yes."

4. The Hotel California Factor

"The designers of Mac - again this is their priesthood - are not thinking about letting their users go," Keanini says. "It's like Hotel California: They are not expecting you to leave."

Companies that move over to the Mac OS X should expect to spend a lot of time converting data if they decide to move back to Windows, Keanini says.

The CTO says that moving all his data back to the Windows platform took more than week. Among the problems: Contacts and appointments exported from the Mac's applications had to cleaned up, he says. Also, there's no simple way to get email out of the Apple Mail application, he says.

"Today, companies need to be thinking about interoperability," he says. "It's the users' data, not the vendor's data."

5. You May Feel the Heat, Literally

Aluminum cases make MacBook Pro laptops, like the one Keanini chose, very sleek. But, Keanini says, the focus on design overlooked the fact that the computers throw off a lot of heat-so much so that he found that he could not use the computer on his lap.

"The religion made me blind," he says. "I was bringing it [the MacBook] on business, but leaving it in the hotel room."

Moreover, the heat causes another problem, he says: The computers' lithium-ion batteries tend to have a shorter lifespan when they run hot. Having to replace the batteries on the laptops more often hit the IT budget bottom line, he says.

Now, the executive runs a Lenovo ThinkPad. "It's a monster, but it runs cool and it's very fast," he says.